This invention relates to a method of manufacture of a dry bearing for high speed, high load purposes.
A lubrication-free or dry bearing such as for example disclosed in Japanese Patent Publication No. 39-16950 is already known. In this Patent Publication, the dry bearing has a porous metallic sintered layer formed from copper or copper alloy powder on a steel plate, with the pores of the sintered layer impregnated with a mixture of polytetrafluoroethylene (PTFE) resin and lead oxide. As shown in FIG. 1, the disclosed dry bearing comprises a porous metallic sintered layer 4 formed on a steel plate 5 and impregnated with PTFE resin 3, in which is dispersed a solid lubricant such as metallic lead 1 in a pulverized form or in a form of masses. The lubricating property of this bearing is enhanced by the PTFE resin and is further improved by the metallic lead 1 in the powdery form or in the form of masses. Thus, this dry bearing has very excellent lubricating property compared to other dry bearings. However, it has been developed in order that it can withstand a load of 1,000 to 1,500 kg/cm.sup.2.m/min in terms of the PV value at the most, so that it can not withstand loads higher than this level. Meanwhile, there are demands for reducing size and weight and increasing speed of automobiles, particularly future automobiles, and this calls for dry bearings capable of withstanding high speed and high load above a PV value of 1,500 kg/cm.sup.2.m/min. Although the prior art dry bearing disclosed in the Japanese Patent Publication No. 39-16950 and shown in FIG. 1 can be used for low speed, low load purposes as noted above, it cannot withstand but would be seized in high speed, high load uses.
In the dry bearing shown in FIG. 1, the metallic lead 1, which is dispersed as solid lubricant in the PTFE resin 3, is not uniformly dispersed. Besides, it is dispersed in a pulverized form or in a form of masses. Further, its melting point is as low as 327.degree. C. Therefore, under high load operating conditions with high peripheral speed and surface pressure and with a PV value higher than 1,500 kg/cm.sup.2.m/min, the pressure on and temperature of the shaft support surface or frictional surface increased so much that the metallic lead 1 is fused and lost. Particularly, as high PV value condition as 3,000 kg/cm.sup.2.m/min cannot be withstood at all. Further, because of the lack of uniformity of the dispersion of the metal, the loss of metal due to fusion does not occur uniformly, leading to local surface portions free from metallic lead 1 even under a condition corresponding to a PV value of about 1,500 kg/cm.sup.2.m/min. In such a case, the load cannot be withstood sufficiently and uniformly, resulting in local aggressive wear.